1. Field of the Invention
The present invention relates to an image processing method and image processing apparatus in which image processing is executed according to distortion correcting data to correct a non-uniform perceived resolution caused by image distortion correction, thereby achieving a uniform perceived resolution over an entire displayed image.
2. Description of the Related Art
In certain types of existing monitoring cameras or on-vehicle cameras, an image of a wide range is captured using a wide-angle lens, and image signal processing is executed to correct image distortion caused by the curvature of the lens and enlarge or reduce a part of the image. For this purpose, wide-angle image distortion correction is executed.
Furthermore, camera signal processing includes aperture compensation. The aperture compensation serves to emphasize a contour of an image so that the perceived resolution of the image will be improved. By adding aperture compensation signals uniformly over the entire image to emphasize a frequency band, it is possible to obtain an image having a uniform perceived resolution over the entire image.
Furthermore, when an image is reduced by electronic zoom, since frequency band regulation is exercised, an aperture compensation is lost in accordance with the reduction ratio. However, when all regions are reduced substantially by the same factor, since an aperture compensation signal is lost uniformly over the entire image, an image having a uniform perceived resolution over the entire image is output.
Japanese Unexamined Patent Application Publication No. 2005-57605 discloses an image processing apparatus that improves image quality by correcting distortion caused in a captured image by such wide-angle image distortion correction. The image processing apparatus includes a correction parameter encoder that encodes a distortion correction parameter for each zoom point indicating a zoom position of an optical zoom mechanism and stores the distortion correcting parameter in a correction memory, a controlling microcomputer that reads distortion interpolation parameters associated with two zoom points corresponding to zoom positions on the basis of coordinate values of a pixel under distortion correction and zoom position information, a zoom interpolator for interpolating the distortion correction parameters that have been read on the basis of phase relationship between the zoom positions, and a correction parameter decoder that decodes the interpolated distortion correction parameter with respect to an x-y direction and supplies the result to an image signal processor. The image processing apparatus executes distortion correction on the basis of zoom positions, using zoom compression parameters obtained by compressing distortion correction parameters for individual lens positions based on zoom segment points.